Studies are in progress to compare the biological activity of C-ASWS with that of coccidioidin and spherulin in immunological assays of guinea pigs infected intratracheally with viable arthrospores of Coccidioides immitis. C-ASWS is isolated from mycelial-phase cell walls of C. immitis by alkaline hydrolysis with 0.5 N NaOH. The cell wall extract is comprised of approximately 80% polysaccharide, 18% protein, and trace amounts of lipid. Two-dimensional immunoelectrophoresis indicates that C-ASWS is a heterogeneous antigen containing 7 components as immunoprecipitates to anti-coccidioidin. Despite this heterogeneity, physiochemical methods have failed to fractionate C-ASWS into a component that is biologically more sensitive or specific than the crude cell wall extract. Immunological assays of experimentally-infected guinea pigs have established that C-ASWS is effective in eliciting in vitro lymphocyte transformation and MIF responses and that the sensitivity of this antigen compares favorably with that of coccidioidin and spherulin. However, lymphocyte transformation assays of healthy, histoplasmin skin-test positive persons showed that all three Coccidioides antigens were highly cross reactive. Studies have been initiated to fractionate C-ASWS using immunoadsorption techniques in an attempt to increase the specificity of this cell wall antigen.